The present invention relates to a monitor for use in continuous feeding of collated articles. Such a monitor is utilized during the course of transporting or feeding of an article such as a metal plate, a printing sheet or a unit thereof to a separate spot of a working machine etc., for judging as to whether articles are correctly and regularly transported one by one or unit by unit.
Generally, it is necessary to detect the occurrence of double feeding during the course of continuous or successive feeding of printing sheet articles one by one or unit by unit. The conventional detecting method is such that each article is measureed in terms of thickness, weight or transmittance of the sheet and the measured value is compared with a given reference value. For example, in a monitor for detecting double feeding of a sheet to a printing machine, generally the doubling detection is based on the fact that double or multiple sheets have a smaller transmittance than a single sheet.
The transmittance of an article is measured by a photocell etc., and the measured value is compared with a given reference value indicative of a normal transmittance of a sheet in the regular feeding. When the measured value falls within a given allowance around the reference value, the judgement is made that the feeding is normally and regularly carried out. If otherwise, the judgement is made that there has occurred erroneous feeding or misfeeding such as doubling or missing of sheets.
However, some types of sheet feeders are used for a collating and bookbinding machine, or a calendar print processing machine. For example, this type of working machine is operated such that different kinds of sheets including a cover, intermediate leaves and photogravure leaves are sequentially fed and recollated in the same order to bind a book. In such a case, the thickness of the sheets varies cyclicly according to the given order in dependence on class or brand of the sheets during the course of continuous feeding of sheets to the working machine. However, the conventional monitor is set with a single reference value, and therefore it cannot monitor the continuous and variable feeding in which the thickness of sheets varies cyclicly according to a given order or sequence.